Droplet Welding, An Environmentally Acceptable Alternative to Soldering for High Strength Electrical Connections

Soldering electronic components to circuit boards involves using environmentally harmful cleaning agents and toxic heavy metals like lead. Solder joints can be unreliable in high shock environments because of non-uniform adhesion. This program will develop an entirely new method for welding such joints. In this novel method, 50-500 nm diam monodisperse droplets of high temperature filler metal are generated remotely and then deposited at the joint to be welded. Almost any metal can be a filler, including the same metal as the those being joined. Droplet size and temperature are controlled so that the depth of the weld and therefore, its relability is also controlled. No flux or cleaning solvent is used in this process. Toxic heavy metal solder is replaced by benign filler metal. Since there is no contact of the energy source with the weld site, thermal or electrical damage to components is eliminated. In Phase I, copper, aluminum, and nichrome wires will be welded to copper foil on a circuit board (copper or aluminum filler). Weld strengths will be measured and correlated with the experimental parameters, droplet metal identity, size, and temperature. In phase II more detailed evaluations will be made to automate and scale-up the method in Phase III follow-on work.